1. Field of the Invention
The present invention relates to a lamp cooling device for cooling a lamp used as a light source and a rear projection display apparatus including the lamp cooling device.
2. Description of the Related Art
FIG. 35 shows an example of the internal structure of a known rear projection display apparatus. The rear projection display apparatus includes a projector 190, a first reflecting mirror 191, a second reflecting mirror 192, and a transmissive screen 193. The projector 190 is arranged in a lower rear portion in a cabinet of the apparatus. The first reflecting mirror 191 is disposed in a lower front portion in the cabinet. The second reflecting mirror 192 is arranged on an inner rear surface of the cabinet. The transmissive screen 193 is disposed in a front surface of the cabinet. A projection lens projects an image, which is generated from a projection image generation unit in the projector 190, onto the first reflecting mirror 191. The projected image is reflected by the first and second reflecting mirrors 191 and 192 and is then formed on the rear of the transmissive screen 193, so that the image is displayed.
This type of rear projection display apparatus can be easily increased in size as compared with a television using a cathode-ray tube because the rear projection display apparatus has a smaller depth and a wider screen. Accordingly, the rear projection display apparatus is becoming widespread as a display of a home theater system. Japanese Unexamined Patent Application Publication No. 11-84533 discloses a rear projection display apparatus having a structure different from that shown in FIG. 35. This apparatus does not include a first reflecting mirror. An image is directly projected from a projection lens to a second reflecting mirror.
Since the rear projection display apparatuses are installed in homes in many cases, each apparatus needs a long-life and high-intensity lamp as a light source. The lamp will now be described.
FIGS. 36 and 37 show a lamp 200 which is generally used in a rear projection display apparatus. The lamp 200 has a light source (also called a burner) 201a, a reflector 202, and a transparent front plate 204. The light source 201a including a glass tube (bulb) filled with a discharge gas is disposed in a space enclosed by the reflector 202 and the transparent front plate 204 such that the light source 201a is isolated. Light emitted from the light source 201a is reflected to the transparent front plate 204 by the inner reflecting surface of the reflector 202. The reflected light is transmitted through the transparent front plate 204 such that the light serves as outgoing light of the lamp 200. In many cases, a curved reflecting surface for collimating the outgoing light as shown by solid arrows in FIG. 37 is used. Some of optical systems each use a curved reflecting surface for converging reflected light once and then diverging the light as shown by dashed arrows in FIG. 37.
Not only light but also a large amount of heat are radiate from the light source 201a, as shown in FIG. 37, of the lamp 200. From the viewpoint of the luminous efficiency and life span of the lamp, it is necessary that the temperature Tb of the light source 201a and the temperature Tc of a sealing portion 201b at one end of the bulb lie in a predetermined range.
For this purpose, a fan 210 is used to blow cold air onto the rear of the lamp 200 in order to cool the lamp 200 as shown in FIG. 36.
However, the intensity of the lamp 200 is increasing in response to requests to increase the brightness of images in the rear projection display apparatus, thus increasing the amount of heat to be exhausted. In the above-described indirect air cooling for the light source 201a and the sealing portion 201b in the lamp 200 whose exterior is blown with air as shown in FIG. 36, it is difficult to set the temperatures Tb and Tc in the predetermined range.
To solve the above problem, a direct air-cooling structure shown in FIG. 38 is proposed. In this structure, the top and bottom surfaces of the reflector 202 have openings 202a and 202b through which the interior space of the lamp is ventilated so that the light source 201a and the sealing portion 201b can be directly air-cooled. Japanese Unexamined Patent Application Publication No. 2003-157715 discloses such a direct air-cooling structure in which the direction of air blowing is opposite to that in the above-mentioned structure in FIG. 38.